Missile autopilot



June 6, 1967 D. E. COLE MISSILE AUTOPILOT Filed July 6. 1961 June 6, E967 D, E. COLE MISSILE AUTOPILOT 3 Sheets-Sheet 2 Filed July 6. 1961 wml amm

v INVENTOR. DONALD E. COLE June 6, 1967 D. E. COLE MISSLE AUTOPILOT 5 Sheets-Sheet Filed July 6, 1961 FVG. 9

TARGET l l I l s REE COIL PLANE 0F WINGS REF AND SIGNAL PHASEVB SIGNAL REF BIAS LEVEL LIFT SECTOR INVENTOR. DONALD E. COLE By @N A PHASE DEMODULATOR OUTPUT DESIRED LnFT QUADRATURE LIFT Ton/EY AGENT United States Patent O 3,323,757 MISSILE AUTOPILOT Donald E. Cole, West Covina, Calif., assignor to General Dynamics Corporation, San Diego, Calif., a corporation of Delaware Filed July 6, 1961, Ser. No. 122,171 Claims. (Cl. 244-3.16)

This invention relates to guided missiles, and more particularly, to a proportional control automatic pilot suitable for controlling the flight path of a rolling type of guided missile.

A rolling type of guided missile wherein the present invention may be employed rotates continually in flight about its longitudinal axis. A pair of laterally opposed, fixed incidence lift producing aerodynamic surfaces, which may y'be readily and rapidly extended into and retracted from the airstream, are provided to achieve directional control. Missile roll is utilized to achieve control in any direction with only one pair of aerodynamic surfaces, thereby enabling a light, simple, reliable control system.

A homing device, such as an infra-red seeker, provides electrical tracking rate information signals. The automatic pilot converts such tracking rate signals into electrical control signals, causing the control surfaces to extend or retract, properly phased in a manner suitable to maneuver the missile to intercept the target. The auto- Imatic pilot of the present invention causes the control surfaces to be extended for a period of time varying linearly with the magnitude of the seeker tracking rate signal. A lift force vector is produced during `a portion of the roll cycle such that a force is applied to the missile to change course toward the target.

Heretofore known control systems for rolling missiles have been of the non-proportional on-off type. A combination of two control signals, one a signal wave and the other a reference wave, is employed to actuate a trigger circuit. The combination signal is compared with a fixed bias voltage in the trigger circuit, which changes condition when the applied signal becomes greater or less than the fixed bias voltage. A square pulse train output signal is produced by the trigger circuit, the Width of the pulses varying in an inverse exponential manner with the amplitude of the applied combined signal.

As a result of the non-linear relationship, a large dead space exists about the zero error point, thereby increasing miss distance due to inability to correct for small errors. Further, missile dynamic stability is decreased, since large control signals are applied suddenly for comparatively small errors.

In contrast, the present Vinvention provides a linear relationship between the period of control surface actuation and the magnitude of the seeker tracking rate signal. As a result, accuracy is improved by reducing miss distance, stresses on the missile are reduced, and effectiveness of the missile is increased.

It is, therefore, an object of this invention to provide a proportional rolling missile control system.

Another object of this invention is to provide a proportional sector autopilot for a rolling type of homing missile.

Another object of this invention is to increase the accuracy of a rolling type of homing missile.

Another object of this invention is to provide an automatic pilot for a rolling type of homing missile.

Another object of this invention is to provide an automatic pilot suitable for a rolling missile, which is simple, reliable, compact, and light in weight.

Other objects and features of the present invention will be readily apparent to those skilled in the art from ice the following specification and appended drawings, wherein:

FIGURE l is an exploded elevation of -a missile utilizing the control system of the present invention;

FIGURE 2 schematically illustrates an optical seeker head which may be employed in this invention;

FIGURE 3 illustrates a reticle forming part of the seeker head;

FIGURE 4 is a simplified diagram of the seeker head spin motor coils and reference coils;

FIGURE 5 is a cross-section of FIGURE 4;

FIGURE 6 is a cross-section of FIGURE 5;

FIGURE 7 illustrates one phase of operation of a magnetic switch;

FIGURE 8 illustrates another phase of operation of a magnetic switch;

FIGURE 9 schematically illustrates the principle of control of a rolling missile with two retractable control surfaces;

FIGURE 10 is a block diagram of an electronic automatic pilot circuit responsive to the seeker head and providing signals to actuate the control surfaces; and

FIGURE 11 is a schematic View of a control surface actuating mechanism.

Referring now to FIGURE l, a rolling missile incorporating the proportional automatic pilot of the present invention includes a seeker 11, an electronics section 12, a control section 13, a warhead 14, and a rocket motor 15. A presently preferred seeker 11, illustrated in FIG- URE 2, is a free gyro stabilized, infra-red sensing mechanism. Seeker 11 provides an output signal representing the angular rate of rotation of the line of sight in space. The entire optical unit 16 rotates, forming a gyroscopic rotor mass. Spherical primary mirror 17 and secondary mirror 18, forming a Cassegrainian type of reflecting telescope, reflect incident infra-red energy `from a target such as a jet aircraft engine through a spinning reticle or chopper 21, illustrated by FIGURE 3, a filter 22, onto stationary infra-red responsive cell 23. Protective dome 24 and filter 22 are transparent to the desired region in the infra-red spectrum, filter 22 being opaque to other regions and serving as an optical band-pass filter.

Reticle 21, functioning in a manner well known to those skilled in the art, enables discrimination against such false targets as cloud edges, and permits sensing of tracking error by chopping the radiation passing to infrared responsive cell 23.

Referring now to FIGURES 4, 5 and 6, illustrated therein are motor coils 26a and 2611, employed to spin the optical head for gyroscopic effect, precession coils 27, and position sensing reference coils 28. A magnetic field actuated switch 31 is provided to alternately energize diametrically opposed motor field coils 26a and 2Gb. A permanent magnet 25, polarized in the plane of rotation, is mounted on parabolic mirror 17 for rotation with the optical system. A ring 32, made of a high permeability material such as the alloy commonly known as mu-metal, picks up flux from the magnet and carries it to magnetic switch 31. Operation of magnetic switch 31 is illustrated in FIGURES 7 and 8. In FIGURE 7, flux collected by ring 32 ows through armature 33 in a direction aiding the normal armature-to-pole gap flux at the right hand side of the armature, and opposing the normal armature-topole gap flux at the left side, resulting in an unbalance of gap forces and closing the right hand gap. This closes the left hand contact, enabling current to flow in coil 26a, repelling the south pole of the rotor and attracting the north pole, resulting in clockwise rotation of the rotor. As the rotor rotates, the posit-ion of the poles changes, as illustrated in FIGURE 8, causing the flux in the armature to reverse, enabling current to flow in coil 26b, resulting in continuing clockwise rotation of the rotor. Switch 31 is positioned a few degrees in advance of the motor coil center line thus compensating for the inertia time constant of the switch armature. The rotor magnet is also phased approximately 30 degrees behind the reference radial on the rotating reticle. One-half of the reticle is 50% transparent, and the other half is furnished with transparent and opaque areas, as illustrated in FIGURE 3. Since the reticle revolves clockwise with the rotor, the reference radial referred to hereinabove is the radius at the right side of FIGURE 3 separating the semi-transparent area from the opaque-patterned area.

Directional control of a rolling missile is accomplished by extending a pair of fixed incidence wings, housed in section 13, during the period of the roll wherein a lift force is furnished to direct the missile to the target. The continuous roll required may be imparted to the missile by means of canted nozzles on the rocket motor, or by canted aerodynamic surfaces such as tail fins.

In the embodiment disclosed herein, the optical system, including reticle 21, is spun at a frequency fo with respect to the target. The missile itself is simultaneously rolling at a rate p revloutions per second to enable production of a lifting force in any direction. Referring to FIGURE 9, the homing head senses the direction of flight path error in polar coordinates referenced to the roll axis of the missile, and extends the control surfaces during the proper portion of each revolution of the missile. A sinusoidal error signal of frequency fo, proportional in amplitude to the magnitude of the olf-axis tracking error, and whose phase indicates the direction of the error, is supplied by the homing head. Reference coils 28, xed to the rolling airframe and sensing the magnetic field of the seeker rotor generates a reference signal fr wing-actuating signal having a frequency and a phase qb, as illustrated in FIGURE 9.

Amplier 34 amplifies the signal generated by sensitive cell 23. Demodulator 35 serves to separate the modulating signal components from the chopper high frequency components of the amplified sinusoidal error signal fo from the infra-red sensitive cell 23. The error signal is applied to precession coils 27 through phase inverter 36 and push-pull power output amplifier 37. Precession coils 27, cooperating with magnet 25, serve to -apply a force to the seeker head when energized by amplified signal fo to rotate the seeker head toward the target.

Signal fo from the demodulator 35 is also applied to signal squaring circuit 41 and to peak detector 42. Squaring circuit 41 serves to convert the sinusoidal signal fo into a square wave having the same frequency and phase relationship. Conveniently, such a squaring circuit may comprise an amplifier and limiter, or an overdriven amplier, as is well known to those skilled in the art. Simultaneously, reference signal fr, having a frequency f, is supplied by reference coils 28 to squaring circuit 44, which may be similar to squaring circuit 41. The square wave from squaring circuit 44 is also applied to phase demodulator 43. Phase demodulator 43 provides ya constant amplitude waveform output signal having the frequency components of a triangular waveform of a frequency ip and phase g5, as illustrated in FIGURE 9. High frequency components are removed by low pass filter 45, leaving the triangular wave signal. The triangular waveform is then applied to a summing circuit 46. Phase demodulator 43 produces a triangular output waveform as long as one of the two input signals is a square wave. The other input signal may be a sine wave. Phase demodulator 43 may be designed to be switched directly by a sine wave reference signal. Thus, squaring circuit 44 may be omitted.

The triangular variable phase signal has a constant amplitude. To provide proportional control, a D.C. bias signal varying proportionally with the seeker tracking rate is required. Peak detector 42, responsive t-o fo from demodulator 35, provides a direct voltage proportional to the amplitude of fo. High frequency components such as detector ripple, seeker noise, and transients are removed from the direct voltage signal by low pass filter 47.

The amplitude-proportional direct voltage and phase proportional triangular voltage are combined in summing circuit 46 and applied to electronic switch 51. The signal applied to switch 51 is a sawtooth; that is, the triangular phasing signal waveform is elevated by the direct voltage bias proportional to amplitude. Switch 51 may conveniently be a Schmitt trigger circuit, of a form well known to the art. Such circuits assume one condition when the applied voltage exceeds a predetermined value, and revert to their quiescent condition when the signal falls below the predetermined value. Conveniently, switch 51 conducts when the instantaneous sawtooth voltage exceeds a predetermined value set by a bias voltage, and cuts off when the instantaneous sawtooth voltage falls below the predetermined value. When switch 51 conducts, wing actuator 52 is energized, and the wings, or control surfaces, are extended.

It will be apparent, therefore, that the control surfaces are extended for 'a period during each revolution of the missile for the time that the sawtooth error signal is greater than the combined bias voltages. The center of the portion of the roll cycle that the control surfaces are actuated coincides with the desired direction 'of lift. Similarly, the length of time the control surfaces are extended, labeled lift sector in FIGURE 9, is proportional to the magnitude of the direct bias voltage from peak detector 42. In addition to a lift force in the desired direction, quadrature lift vectors on either side are also produced. However, these forces are equal and opposite, and cancel out. A large portion of the actual lift force is produced yby the missile body, the wings, or more properly, control surfaces, serving mainly to change the angle of incidence of the elongated missile body. The angle of incidence of the body axis with respect to the flight path results in lift, deflecting the iiight path toward the desired path. The lead angle of the reference coil, disclosed hereinabove, is provided to compensate for the time lag required for the Wing actuating mechanism to extend yand retract the control surfaces and to compensate for the phase lag in the filter following the phase demodulator, thereby enabling the net l-ift force `of the control surfaces plus the body to act in the direction lof the target.

Wing actuator 52 may be any convenient type of on-oif servo system. Hydraulic or pneumatic system may be employed, with an electrically loperated control valve actuated by switch circuit 51. Preferably, however, electrical actuating means are employed. A suitable electrical actuator is schematically disclosed by FIGURE 11. A coil 53, connected to, and energized by, switch 51, pulls solenoid core 54 downwardly against tension spring 55. A yoke 56, connected to core 54, engages pin 57 on sector gear 61, rotating sector gear 61 about pivot 62. Sector gear 61 meshes wit-h gear 62, journaled about pivot 63 and fastened to wing 64. Rot-ation of gear 62 results in extension of wing 64. Wing l65 is similarly rotated into the extended position by gear 66 and sector gear 67. When switch 51 is in the off position, spring 55, extended by solenoid core 54, returns core 54 to its normal position, retracting wings 64 and 65.

While a presently preferred embodiment -of this invention has been disclosed hereinabove, it is understood that the invention is not limited thereto since many variations will be readily 'apparent to those -skilled in the art, and is to be limited only by the scope of the appended claims.

What 4is claimed is:

1. In a rolling missile having a target seeker adapted to track a target and generate a first signal having a phase indicating the direction of tracking error and amplitude indicating the magnitude of tracking ernor and a second `signal having a reference phase, the combination of wave squaring means responsive to said first signal, a phase detector responsive to said second :signal -and connected to said wave squaring means to generate a triangular wave signal, amplitude detecting means responsive to said first signal for providing a direct voltage having a magnitude proportional to the amplitude of said first signal, electronic switch means connected to said phase detector and to said amplitude detecting means for providing a control actuating signal at a time determined by the phase of said triangular wave and for a period determined by the magnitude of said direct voltage.

2. In a rolling missile having a target seeker adapted to track a target land generate a first signal having a phase indicating the direction of tracking error and amplitude indicating the magnitude of tracking error and a ysecond signal having a reference phase, the combination of wave squaring means responsive to said first signal, a phase detector connected to said wave squaring means and responsive to said second signal to generate a triangular wave signal, amplitude detecting means responsive to said first signal for providing a direct voltage having a magnitude proportional to the amplitude of said first signal, an electronic switch connected to said phase detector and to said amplitude detecting means for providing a control actuating signal at a time determined by the phase of said triangular wave and for a period determined by the magnitude of said direct voltage, and controlsurface actuating means connected to said electronic switch.

3. In a rolling missile having an independently movable target seeker adapted to track a target and generate a first signal having a phase indicating the direction of tracking error and amplitude indicating the magnitude of tracking error and a second signal having a reference phase, and having seeker aiming means, the combination of means for applying said first signal to said seeker aiming means, wave squaring means responsive to said first signal, a phase detector responsive to said second signal yand connected to said wave squaring means to generate a triangular wave signal, amplitude detecting means responsive to said first signal for providing a direct voltage having a magnitude proportional to the amplitude of said first signal, an electronic switch connected to said phase detector and to said amplitude detecting means for providing a control actuating signal at a time determined by the phase of said triangular wave and for a period determined by the magnitude of said direct voltage, and control surface actuating means connected -to said electronic switch.

4. In a rolling missile having an independently movable target seeker adapted to track a target and generate a first signal having a phase indicating the direction of tracking error and amplitude indicating lthe magnitude of tracking error and a second signal having a reference phase, and having seeker aiming means, the combination of an amplifier and detector connected to said first signal, means connecting said detector to said seeker aiming means wave squaring means connected to said detector, -a phase detector connected to said wave squaring means and responsive to said second signal to generate a triangular w'ave signal, -amplitude detecting means responsive to said first signal for providing a direct voltage having a magnitude proportional to the amplitude of said first signal, an electronic switch connected to said phase detector and to said amplitude detecting means for providing a control actuating signal at a -time determined by the phase of said triangular wave and for a period determined by the magnitude of said direct voltage, and

6 control surface actuating means connected to said electronic switch.

5. 'In a rolling missile having an independently movable target seeker adapted to track a target and generate a first signal having a phase indicating the direction of tracking error and amplitude indicating the magnitude of tracking error and a second signal having a reference phase, and having seeker aiming means, the combination of an amplifier responsive to said first signal, a first detecto-r connected to said amplifier and having an output connected to said seeker aiming means, wave squaring means responsive to said first detector, a phase detector connected to said wave squaring means and responsive to said second signal to generate a triangular Wave signal, amplitude detecting means responsive to said first signal for providing a direct voltage having a magnitude proportional to the amplitude of said first signal, an electronic switch connected to said phase ldetector and to said amplitude detecting means for providing a control actuating signal at a time determined by the phase of said triangular wave and for a period determined by the lmagnitude of said direct voltage, and control surface actuating means connected to said electronic switch.

6. In a rolling missile having an independently movable target seeker adapted to track a target and having a target radiation sensitivity ycell to generate a lfirst signal having a phase indicating the direction of tracking error vand amplitude indicating the magnit-ude of tracking error, and a reference coil to generate a second signal having a reference phase, a precession coil to aim said target seeker at said target, the combination of wave squaring means responsive to said first signal, a phase detector connected to said wave squaring means and responsive to said second signal to generate a triangular wave signal, amplitude detecting means responsive to said first signal for providing a direct voltage having a magnitude proportional to the amplitude of said first signal, an electronic switch connected to said phase detector and to said amplitude detecting means for `providing a control actuating signal at a time determined by the phase of said triangular wave and for a period determined by the magnitude of said direct voltage, and control surface actuating means connected to said electronic switch.

7. In a rolling missile having an independently movable target seeker adapted to track a target and having a target radiation sensitive cell to generate a first signal having a phase indicating the direction of tracking error and amplitude indicating the magnitude of tracking error, and a reference coil to generate a second signal having a `reference phase, a precession coil to aim said target seeker at said target, the combination of an amplifier connected to said radiation sensitive cell, a first detector connected to Said amplifier, wave squaring means oonnected to said first detector, a phase detector connected to said first detector, a phase detector connected to said wave squaring means and responsive to said second signal to generate a triangular wave signal, amplitude detecting means responsive to said rst signal for providing a direct voltage having a magnitude proportional to the amplitude of said first signal, an electronic switch connected to said phase detector and to said amplitude detecting means for providing a control actuating signal at a time determined lby the pfhase of said triangular Wave and for a period determined by the magnitude of said direct voltage, and control surface actuating means connected to said electronic switch.

8. In a rolling missile having an independently movable target seeker adapted to track a target and having a target radiation sensitive cell to generate a first signal having a phase indicating the direction of tracking error and amplitude indicating the magnitude of tracking error, and a reference coil to generate a second signal having a reference phase, a precession coil to aim said target seeker at said target, the combination of an amplifier connected to said radiation sensitive cell, a first detector connected to said amplifier, Wave squaringmeans connected to said first detector, a phase detector connected to said wave squaring means and responsive to said second lsignal to generatea triangular wave signal,y a peak detector y responsive to said first signalfor providing adirect voltage having a magnitude proportional to the amplitude of said iirst signal, an electronic yswitch connected to said phase detector andto said peak detector tor providingar control actuating signal at a time determined 'Dy the phase of said triangular wave and for a period determined by the magnitude of said direct voltage.,k and control snr;-

face actuating means connected to said electronic switch.

9. In -arolling missile having'an independentiymovable target seeker adapted to track al targetand havingk a target radiation sensitive cell to generate a rst signal having aphase indicating the direction of tracking errorA and amplitude indicating the magnitude of traekingerror,l anda reference-coil to generate asecondsignal having a reference phase,k a precession coil to aim said target .seeker at said target, the combination of an amplitier connectedto said radiation `sensitive cell, garst detector connected to said amplifier, Wave squaring means ign-k cluding a limiter connected to saidrst detector, aphase detector connected to said Wave squaring means and responsive to said. secondsignal to generate a triangular wave signal, 'a peak detector connected lto said `irst de.-

tector Ifor providing a direct volt-age having a magnitude proportional to the amplitude of said. first signal, an elec- I tronic switch connected to saidA phase-detector and to said peak detector for providing `a control actuating signal at a timedetermined bythe phase of said triangular Wave and for a period determined 'by the lmagnitude off said directvoltage, and control surface actuating means connected to said electronic switch. t

- .a reference phase, a precession coil to aim `said .targetl -Seeker at said target, thecombination of an amplifier connected to said'radiation sensitive cell, a first detector connected totsaid amplifier, Wave lsquaring means linclud-y ling an amplifier and .limiter connected to ysaid first ltie-- tector, a phase detector connected lto saidl WaveA squaring l means and responsive to said second signal to generate a triangular Wave' signal, al peak detector connectedtto lsaid irst detector for providing a direct voltage having'a magf nitude'proportionalto the amplitude of said iirst signal,

t anelectron'ic switch connected to said phase detector and to said `peak detector for providing a control actuating ksignal at aj time determinedby the phase of said tri= angular Waveand/for a period determinedby themagni tudeof said direct voltage, and electromagnetic control i surface actuating meanshaving a coil connectedto said i lelectronic switch.

l No references cited.`

` `i:;,i\nA1\/1IN A.. BROCHELT, Primary Examiner.

CHESTER L. JUsrUs,k SAMUEL PEINBERG,

Examiners.

i A.`E.'HALL,l L; L. HALLACHER, W. C, ROCH,

Assistant Examiners.' 

1. IN A ROLLING MISSILE HAVING A TARGET SEEKER ADAPTED TO TRACK A TARGET AND GENERATE A FIRST SIGNAL HAVING A PHASE INDICATING THE DIRECTION OF TRACKING ERROR AND AMPLITUDE INDICATING THE MAGNITUDE OF TRACKING ERROR AND A SECOND SIGNAL HAVING A REFERENCE PHASE, THE COMBINATION OF WAVE SQUARING MEANS RESPONSIVE TO SAID FIRST SIGNAL, A PHASE DETECTOR RESPONSIVE TO SAID SECOND SIGNAL AND CONNECTED TO SAID WAVE SQUARING MEANS TO GENERATE A TRIANGULAR WAVE SIGNAL, AMPLITUDE DETECTING MEANS RESPONSIVE TO SAID FIRST SIGNAL FOR PROVIDING A DIRECT VOLTAGE HAVING A MAGNITUDE PROPORTIONAL TO THE AMPLITUDE OF SAID FIRST SIGNAL, ELECTRONIC SWITCH MEANS CONNECTED TO SAID PHASE DETECTOR AND TO SAID AMPLITUDE DETECTING MEANS FOR PROVIDING A CONTROL ACTUATING SIGNAL AT A TIME DETERMINED BY THE PHASE OF SAID TRIANGULAR WAVE AND FOR 